The present invention relates to a plastic blind rivet suitable for attaching an attaching part to a member being attached to, such as a panel.
A blind rivet is comprised of a rivet body comprising a hollow tubular sleeve and, at one end of that sleeve, a hollow flange formed so as to have a large diameter, and a mandrel that passes through the rivet body to extend out from the flange and that has a head, of larger diameter than the inner diameter of the sleeve, at the end of the sleeve that is opposite the flange. To fasten the blind rivet, the rivet body, having the mandrel passed through it, is inserted, mandrel head first, into an attachment hole in an attaching part that has been placed on a member being attached to, so as to line up with its attachment hole until the mandrel head protrudes from the back side of the member being attached to, and the sleeve flange is flush against the attaching part. Next, using a fastening tool, the mandrel portion extending out from the flange on the attaching part side is pulled out from (relative to) the flange with such force that it breaks. As a consequence of that pulling out, the portion of the sleeve on the back side of the member being attached to is expanded; whereupon, the blind rivet is fastened to the member being attached to and the attaching part, with that member being attached to and that attaching part clamped between the expanded portion and the flange, so that the attaching part is coupled to the member being attached to.
The most commonly used blind rivets are made of metal, but plastic blind rivets are also known, as described in Patent Literature 1 and Patent Literature 2. Compared to a metal blind rivet, a plastic blind rivet has the advantages of being light in weight and easy to machine, but, on the other hand, suffers such disadvantages as that when the sleeve of the rivet body expands, it is not easy to achieve the expansion deformation at the desired position without the sleeve breaking, and it is not easy to obtain a fastening of the desired strength. Also, in cases of plastic deformation that exceeds the limitations of the plastic material, there is a danger of problems such as cracks* occurring. To prevent cracks, plastic materials exhibiting good elongation (such as Nylon) are selected. With Nylon or the like, however, the elongation performance during drying becomes poorer than the performance when water (humidity) is being supplied. For that reason, it is necessary to continually supply water (humidity) in order to maintain constant elongation performance, which results in increased cost, and, in addition, the fastening force thereof will be affected by such environmental factors as humidity and so does not stabilize.
Prior art literature includes: Patent Literature 1, TOKKAI [Unexamined Patent Application] No. S55-065710/1980; and Patent Literature 2, TOKKAI No. S61-013012/1986. With the plastic blind rivets described in Patent Literature 1 and Patent Literature 2, latching grooves (or latching projections) are formed in multiple stages in the axial direction of the outer circumferential surface portion of the mandrel corresponding to the sleeve thereof, and latching projections (or latching grooves) are formed in multiple stages in the axial direction on the corresponding inner wall surfaces, thus making provision so that the expansion deformation can be maintained at the desired position when the sleeve of the rivet body expands. However, the formation of latching grooves and latching projections in multiple stages in the axial direction on the outer circum-ferential surface of the mandrel and inner wall surfaces of the sleeve involves complex molding, and machining is no longer easy.
In the plastic blind rivets described in Patent Literature 1 and Patent Literature 2, furthermore, there are slits that extend in the longitudinal direction of the sleeve, formed to facilitate sleeve expansion; however, in order to effect expansion at the desired position, the slits are not formed with constant widths along their entire length, but rather are formed so that some portions thereof, in the longitudinal direction, are of different width than other portions. When the slits in the sleeve are not formed with constant widths, however, molding becomes complex, and machining is no longer easy.